Deflection safety control for platform of vertical rising lift

ABSTRACT

A deflection safety control for the platform of a scissors lift comprises a pendulum mounted on the platform and having a switch actuated by a part of the pendulum extending above the pivot point.

United States Patent 1191 Richards 1 Sept. 17, 1974 DEFLECTION SAFETYCONTROL FOR PLATFORM OF VERTICAL RISING LIFT [75] Inventor: Lawrence 1.Richards, Elk Grove Village, 111.

[73] Assignee: Autoquip Corporation, Chicago. 111.

[22] Filed: Apr. 13, 1973 [21] Appl. No.: 350,678

[52] US. Cl. 182/19, 182/141 [51] Int. Cl. E04g 1/18 [58] Field ofSearch 182/19, 18, 141, 148;

[56] References Cited UNITED STATES PATENTS 2,773,953 12/1956 Lawick..200/61.51

3,228,659 1/1966 Sturm 182/18 3,451,029 6/1969 3,590,948 7/19713,791,484 2/1974 Harrison 182/2 Primary Examiner-Reinaldo P. MachadoAttorney, Agent, 0) Firm-Darbo, Robertson & Vandenburgh [57] ABSTRACT Adeflection safety control for the platform of a scissors lift comprisesa pendulum mounted on the platform and having a switch actuated by apart of the pendulum extending above the pivot point.

5 Claims, 3 Drawing Figures DEFLECTION SAFETY CONTROL FOR PLATFORM OFVERTICAL RISING LIFT BACKGROUND AND SUMMARY OF THE INVENTION Verticallifts comprising a platform raised and lowered by a suitable power meansare employed for many applications. Some of these would perhaps beclassed as elevators while others might be called dock lifts, etc. Inmany instances the motive power device is not one that would absolutelyensure that the platform remain level under all conditions of loading.For example the motive power device might be a hydraulic ram centeredunder the platform. Another example might be the so-called scissors liftcommonly employed for dock lifts or the like, particularly where thelift is adapted to be moved from one location to another. While theselifts are made more than adequately strong for their intended purpose,it is possible that they can be abused in a manner such that theplatform tends to tip to one side to an extent that the power device,etc., is damaged and perhaps even creating a dangerous situation so faras the workers involved are concerned. For example, there have beenoccasions when a scissors type dock lift was carelessly operated in amanner such that, as the platform was being raised to unload a truck, aside of the platform was caught under the truck. Since the situation wasnot noticed by the operator, the operator continued to endeavor to raisethe lift, the result being that the platform was canted to such anextent that structural damage resulted. It is not inconceivable that asimilar situation could occur as a result of excessive uneven loading ofobjects being supported on the platform. With a hydraulic ram type lift,such excessive uneven loading can cause deflection in the ram and damageto the bearing about the ram.

The present invention relates to a simple and effective control for usewith the platform of a vertically moving lift to prevent the lift frombeing operated under conditions creating excessive deflection of theplatform.

Utilizing the present invention the power movement of the lift is shutoff when excessive deflection occurs. Thus, using the example previouslygiven, if the platform of the dock lift were caught under a truck, theoperator would be unable to further raise the platform after apredetermined degree of deflection had occurred. If such a lift restingon the floor were unevenly loaded to an extent such that excessivedeflection and damage could result, the power apparatus could initiallybe actuated to start raising the lift, but as soon as the lift wereraised sufficiently to allow deflection in excess of the predeterminedamount to occur, the power operation would be shut down. Just what isexcessive deflection will be determined with regard to the particularlift being protected. For example, in the dock lift hereinafterdiscussed, upon reaching a 6 inch deflection in one side of the platformthe elastic limit will be reached and structural damage will occur.Therefore the safety device is set to prevent operation beyond the pointat which a three inch deflection occurs. Provision is made in accordancewith the present invention so that this determination can, if desired,be made empirically by the field adjustment of the amount of deflectionthat will occur before the power is shut off.

An important advantage of this invention is the simplicity of itsembodiments as compared to alternative devices (e.g. strain gauges) thatmight be used. It is a very simple matter to connect these embodimentsinto each of the variety of control circuits that might be employed withvarious types of lifts.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a liftembodying the invention;

FIG. 2 is an enlarged side view of the embodiment incorporated in FIG.1; and

FIG. 3 is a front view as seen at line 33 of FIG. 2.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure is offeredfor public dissemination in return for the grant of a patent. Althoughit is detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept therein no matter how others may later disguise itby variations in form or additions or further improvements.

For the purposes of illustration, a scissors type dock lift isillustrated. This comprises a base 10, a platform 11 having ramps 12thereon. Connecting the base and the platform are a pair of scissorsdevices 13, each scissors device being positioned at a respective side(of a pair of opposite sides) of the platform. The vertical movement isachieved by a pair of hydraulic rams 14 interconnecting the base and theframe of the platform 11. A hydraulic pump, etc., not shown, isconnected to the rams 14 and is controlled by a suitable set of controls15. The platform 11 includes as a part of its frame structure a housingpositioned at one end of the platform and having a wall 16 transverse tothe sides at which the scissors devices 13 are located. The hydraulicapparatus and controls are mounted in the housing.

As thus far described, the structure represents known apparatus uponwhich the present invention is an improvement.

The illustrated embodiment of the present invention comprises a frame 20secured'within the housing as by means of bolts 21 and positionedbetween the two sides at which the scissors devices 13 are located.Pivotally mounted on this frame is a pendulum, generally 22, whichoperates a control switch, generally 23. The pendulum comprises a rod 25formed about an axis 26. Intermediate its ends it is pivotally mountedon a bolt 27 secured to frame 20, the bolt defining a pivotal axisintersecting wall 16. A suitable antifriction bearing 28 is provided onthe bolt. The lower end of the rod 25 is secured to a weight 29. Theupper end of the rod has a surface in the form of a shallow Vsymmetrical with respect to axis 26 (i.e., each side is a mirror imageof the other).

The switch 23 includes a body 32 secured to frame 20 by four bolts 33.Provision is made so that there can be vertical adjustment of the switch23 with respect to the pendulum 22 or vice versa. In this embodiment,such provision takes the form of slots 34 in frame 20 through whichslots the bolts 33 extend. This permits the bolts 33 (and the switchbody 32) to be moved vertically on the frame. When the bolts 33 aretightened, the switch 23 remains in that position.

In actual practice, the mechanism of switch 23 would comprise asnap-action switch, represented by those sold under the trademarkMicroswitch, however, for the purposes of illustration, merely a pair ofswitch contacts 37 are shown. This switch has an actuating member in theform of a plunger 35 with'a wheel 36 on the distal end thereof to movethe upper contact with respect to the lower contact when the plunger ismoved. As indicated by the dotted line 38, this switch is connected tothe controls for the hydraulic system so as to shut clown the operationof hydraulic cylinders 14 in the event of excessive deflection ofplatform 11.

For example, assume that the near right side of platform 11 as viewed inFIG. 1 (it would be the right hand side as viewed in FIG. 3 if one couldsee it) is excessively loaded so that that side of the platfonn issubstantially lower than the opposite side of the platform. This wouldcause the pendulum to move so that the rod assumed the positionillustrated at 25 in FIG. 3. The result would be that the surface on theupper end of the rod would act as a cam and the wheel 36 act as a camfollower to move the plunger 35 upwardly, causing switch contacts 37 toopen. Thereupon the controls 15 would prevent further movement of thehydraulic rams 14. Were the uneven loading to occur at the opposite sideof platform 11, the rod of the pendulum would assume the positionindicated at 25" and the same result would occur, namely the shuttingdown of the hydraulic rams 14. In any event, when the uneven loading iscorrected, the pendulum 22 would move sufficiently back toward itsvertical position to permit switch contacts 37 to close so that theoperation of the hydraulic rams 14 can be resumed. By adjusting thespacing of the switch with respect to the pendulum, one can vary theamount of movement of the pendulum required to actuate the switch.

From the foregoing description, obvious variations will be apparent tothose skilled in the art. For example, the switch 23-could be a normallyopen switch rather than the normally closed switch and the contacts thenclosed by the tipping of the pendulum. The end 30 of the rod could be aninverted V, or even a segment of a cylinder, rather than the shallowupright V as illustrated and described.

In a specific embodiment employed with a dock lift as illustrated, thetotal length of the pendulum was 29 inches, the pivotaxis (bolt 27) was4 /2 inches from the nearest part of the end 30. The angle between thetwo sides of the end 30 was 140. The switch 23 was a Square D, typeBSlD.

I claim: I

1. In a hydraulically powered vertical lift having a platform structurewhich may be unevenly loaded to an extent sufficient to damage thestructure, which lift has hydraulic control means, the improvementcomprising the combination with said lift of:

a frame mounted on said structure;

a pendulum device pivotally mounted on said frame for pivotal movementabout an axis whereby deflections of the lift cause the pendulum deviceto move through angles which are a function of theextent of deflection;

control switch means operatively connected to said device to be actuatedby a movement of the pendulum device through a predetermined angle; and

means connecting the control switch means and the hydraulic controlmeans to deactivate the application of hydraulic power when said controlswitch means is so actuated.

2. In a vertical lift as set forth in claim 1, wherein the platform hastwo opposite sides and an end and a wall at said end transverse to saidsides, said lift including scissors means at said sides respectively,said device being mounted on said wall with said axis intersecting saidwall. a

3. In a vertical lift as set forth in claim 1, wherein said deviceincludes an upright rod having an axis, a weight at the lower end of therod, and a pivotal mounting on said axis intermediate the ends of therod, the upper end of the rod having portions at each side of the axiswhich are mirror images of each other and are at different distancesfrom the pivotal mounting than is the distance along said axis to thepivotal mounting;

said switch means having an actuating member in contact with said upperend of the rod, said actuating member being movable toward and away fromsaid pivotal mounting to actuate the switch means.

4. In a vertical lift as set forth in claim 3, wherein one of the saidswitch means and the pivotal mounting is movable with respect to theother so that an adjustment may be made as to the size of saidpredetermined angle required to actuate the switch means.

5. In a vertical lift as set forth in claim 3, wherein said upper end isin the form of a shallow V.

1. In a hydraulically powered vertical lift having a platform structurewhich may be unevenly loaded to an extent sufficient to damage thestructure, which lift has hydraulic control means, the improvementcomprising the combination with said lift of: a frame mounted on saidstructure; a pendulum device pivotally mounted on said frame for pivotalmovement about an axis whereby deflections of the lift cause thependulum device to move through angles which are a function of theextent of deflection; control switch means operatively connected to saiddevice to be actuated by a movement of the pendulum device through apredetermined angle; and means connecting the control switch means andthe hydraulic control means to deactivate the application of hydraulicpower when said control switch means is so actuated.
 2. In a verticallift as set forth in claim 1, wherein the platform has two oppositesides and an end and a wall at said end transverse to said sides, saidlift including scissors means at said sides respectively, said devicebeing mounted on said wall with said axis intersecting said wall.
 3. Ina vertical lift as set forth in claim 1, wherein said device includes anupright rod having an axis, a weight at the lower end of the rod, and apivotal mounting on said axis intermediate the ends of the rod, theupper end of the rod having portions at each side of the axis which aremirror images of each other and are at different distances from thepivotal mounting than is the distance along said axis to the pivotalmounting; said switch means having an actuating member in contact withsaid upper end of the rod, said actuating member being movable towardand away from said pivotal mounting to actuate the switch means.
 4. In avertical lift as set forth in claim 3, wherein one of the said switchmeans and the pivotal mounting is movable with respect to the other sothat an adjustment may be made as to the size of said predeterminedangle required to actuate the switch means.
 5. In a veRtical lift as setforth in claim 3, wherein said upper end is in the form of a shallow''''V.''''